The present invention relates generally to a bone cement composition, a kit and a method of making the bone cement composition.
Any publications or references discussed herein are presented to describe the background of the invention and to provide additional detail regarding its practice. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.
Bone cement compositions are useful in applications such as dental and medical procedures. In particular, they are frequently used in bonding or affixing an implant material to natural bone and to repair damaged natural bone.
Typically, current bone cement compositions are sold in two-part preparations containing a powder (or dry) part and a liquid (or wet) part, which, when combined, polymerize to form a hardened substance mimicking many of the physical properties of natural bone. The powder part typically includes a polymeric material, such as acrylate polymers, while the liquid part includes a reactive monomer, such as methylmethacrylate. Recent developments have focused on modifying the bone cement composition for particular medical procedures.
For example, to attach prostheses to bone, Faccioli et al. (U.S. Pat. No. 5,004,501) discloses a bone cement composition having a polymer with submicron particle size, i.e. less than 0.9 microns. As stated in Faccioli et al., the function of the submicron particles is to fill any voids left in the bone cement composition to produce stronger bone cement. The patent further discloses the use of fluoride salts to produce a stronger bond between the bone cement and the bone of the patient.
For particular medical applications such as vertebroplasty, manufacturers have turned to producing bone cement compositions having radiopacity and longer setting times. For example, Lavergne et al. (U.S. Patent Application No. 2005/0256220) describes a polymethyl methacrylate (PMMA)-based bone cement having setting times greater than 15 minutes and a high concentration of a radio-opaque component, and optionally calcium phosphate.
In another example of bone cements for vertebroplasty procedures, Voellmicke et al. (U.S. Pat. No. 7,008,433 and U.S. Patent Application No. 2003/0032964) describe a PMMA-based composition to provide radiopacity and further increase the setting time of the bone cement. Specifically, the bone cement composition has a setting time that is at least greater than 18 minutes. To produce a bone cement with a higher setting time and increased radiopacity, Voellmicke et al. use barium sulfate at amounts of 20% by weight to 40% by weight. The barium sulfate particles have D50 sizes of greater than 3 microns and require 50% of the barium sulfate particles to be unbound (i.e. free) from the PMMA particles.
Other applications have focused on increasing the viscosity of the bone cement composition at an accelerated rate to infiltrate the medical site and prevent any migration of the cement during medical procedures. In particular, Beyar et al. (U.S. Patent Application Nos. 2007/0027230 and 2007/0032567), focus on a viscosity greater than 500 Pascal-second at 2 minutes after the initiation of mixing the two components of the bone cement composition. The U.S. Patent Applications of Beyar et al. claim to achieve a high viscosity at an expedited rate by using one or more sub-population of PMMA beads with a molecular weight that is significantly different than a main population of PMMA beads. In general, the PMMA beads are incorporated into a cement by polymer growth and attachment initiated through the double bond of a monomer and/or on the surface of the PMMA beads and the presence of an initiator.
Other U.S. patents and publications describing various tools, cements and methods for treating bone include, U.S. Pat. No. 4,494,535, U.S. Pat. No. 4,653,487, U.S. Pat. No. 4,653,489, U.S. Pat. No. 4,969,888, U.S. Pat. No. 5,108,404, U.S. Pat. No. 5,276,070, U.S. Pat. No. 5,336,699, U.S. Pat. No. 6,383,188, U.S. Pat. No. 6,383,190, U.S. Pat. No. 6,348,055, and U.S. Patent Publications 2003/0109883; 2002/0068974; 2004/0260303; and 2007/0087031.
While there have been attempts to reduce cement leakage by injecting more viscous cement, for example, during the doughing time, the hardening time of PMMA cements is still considered to be too long. In addition, typical PMMA formulations result in a failure strength material that has been reported to over compensate the augmented vertebra which then in turn increases the probability of failure in adjacent vertebrae. Hence, it would be desirable to provide a fast setting bone cement with a lower failure strength, and or improved osteoconduction.